While this won't be an issue for me, I'm sure many of our readers might have the hardware that will make it an issue for them.
One of the more common questions I hear about Vista is which bit version of Windows Vista should one get. Do we go with x86 32 bit edition or x64 64 bit edition? I'm going to try to clear that question up as best as I can and explain the pros and cons of each choice.
First we must understand a little background on what x64 is. X64 is the 64 bit extension technology that AMD invented (AMD64) to seamlessly migrate the 32 bit x86 (as in 286, 386, 486 compatible microprocessors) world into a 64 bit era. Intel in partnership with HP had refused to extend the ancient x86 platform and had already committed to its all new pure 64 bit IA-64 Itanium architecture...
from http://www.edbott.com/weblog/